1. Field of the Invention
This invention concerns wireless communication networks, particularly a process and system for preserving connectivity among nodes in a network as the topology of the network changes over time.
2. Discussion of the Known Art
So-called point to multipoint or PMP equipment is used often in broadband wireless network applications. Typically, the equipment is standards based or certified by an industry trade group, e.g., WiMAX Forum certified™, IEEE 802.16-2004™ (hereafter “802.16d”), IEEE 802.16e-2005™ (hereafter “802.16e”), or HIPERMAN. Mesh and mobile ad hoc network (MANET) systems are also used, especially in networks deployed for the military. An example of a mesh network resides in the mentioned 802.16d standard which defines a mesh mode of operation. The mesh mode defined in 802.16d is not capable of interoperating with the PMP mode defined in the standard, however. That is, users must elect to use only one of the two modes for operation in the network, and the standard does not suggest a process by which the operating mode of a network can change from PMP to mesh or vice versa over time during operation of the network
Because allocations of radio frequency (RF) spectrum for wireless networks are generally difficult to obtain, it would be desirable for this and other reasons to be able to implement multiple operating protocols (e.g., PMP, mesh and MANET) at given times over a single network channel. For example, a node may be needed to perform the role of a relay station in order to extend the coverage of an existing PMP base station to subscriber stations that have moved out of the base station's range. In another example, two military convoys may have established their own PMP networks to maintain wireless connectivity among vehicles of the respective convoys while in motion. When mobile base stations of the two networks pass near one another, it would be desirable for the base stations to instantiate a MANET to be able to coordinate among themselves, while maintaining the roles of PMP base stations for serving the vehicular subscribers in the respective convoys.
As in the last example above, mobile military operations typically involve a significant change in network topology during the course of a mission. That is, at the start of the mission, elements of a military unit that operate as nodes of a network are usually gathered close to one another at their base. At this phase, a PMP network protocol offers an advantage of efficient use of network capacity. As the elements (i.e., nodes) of the network leave their bases and the mission unfolds, their motion generates continuous changes in the topology of the network and often adversely affects their connectivity among one another.
In another example, a military training exercise may require collection of performance data from thousands of RF devices in the field, and each soldier may be provided with a wireless device for relaying data he or she collects during the exercise. While the soldier devices would operate most efficiently in a PMP network environment, one or more of the devices may be outside the coverage of a PMP base station but must nonetheless forward the data wirelessly to the base station. In such a case, it would be desirable if the out-of-range devices could connect with an active subscriber station within range of the devices, and for the subscriber station to assume the role of a base station with respect to the devices so as to forward the data collected by the devices to the actual base station of the PMP network. Such a procedure may be implemented only if one or more of the subscriber stations of the PMP network are capable of changing their roles so as to adapt to changes in location of other nodes in the network.
That is, if nodes in a mobile unit's network are capable of changing their roles dynamically from that of, e.g., a PMP base or subscriber station to that of a mesh node, connectivity among all the nodes in the network may be maintained more effectively. While the network may possibly evolve during the course of a mission from fully PMP to fully mesh operation, it would likely need to support a mixture of the two modes at any given time during the mission. When the mission is completed and all the nodes return to their bases, the network may resume a fully PMP mode of operation.
U.S. Pat. No. 7,031,274 (Apr. 18, 2006) discloses a method of enabling systems following a known IEEE 802.11 protocol to interoperate with wireless local area networks (WLANs) that use an otherwise incompatible HIPERLAN/2 standard, on a common transmission channel. Further, U.S. Pat. No. 7,133,381 (Nov. 7, 2006) describes a method by which stations operating under an enhanced, IEEE 802.11e standard, can prevent interfering transmissions from stations that do not practice the enhanced standard.
International Application No. PCT/US/2007014386 filed Jun. 20, 2007, and assigned to the assignee of the present application and invention, discloses signal framing structures that may be used in a PMP configured network so as to implement MANET protocols in conjunction with PMP protocols. All relevant portions of the mentioned '386 PCT application are incorporated by reference.